The present invention relates to a high-density multi-layered printed wiring board having a hole having a diameter of 25 to 200 xcexcm and having at least three copper foil layers, which printed wiring board comprises a copper-clad multi-layered board in which all connections between copper foil layers are done with a through-hole penetrating through each of the copper foil layers. Further, the present invention relates to a method of producing a printed wiring board by using a copper-clad board which is prepared by disposing a hole-making auxiliary material on a copper surface of a multi-layered board having at least three copper foil layers, processing a hole formation in the outer and internal copper foil layers by direct irradiation with a high-output carbon dioxide gas laser to form a penetration hole for a through hole. Thereafter, the internal and outer layer copper foil burrs are removed from the hole portions, by etching while at the same time, the outer copper foil layers on the front and reverse surfaces are etched two-dimensionally to remove parts of the outer copper foil layers to reduce the thickness of the outer copper foil layers. Copper plating is then carried out. Furthermore, the present invention relates to a method of producing a printed wiring board which uses a resin composition having a carboxyl group in its molecule as an auxiliary material for forming a hole.
The multi-layered printed wiring board obtained by the present invention has a small-diameter hole and is used mainly for a novel semiconductor plastic package as a high-density small-sized printed wiring board.
In a high-density printed wiring board used for a semiconductor plastic package, a penetration hole for a through hole is conventionally made with a drill. In recent years, the through hole diameter is decreasing to 180 xcexcm or less, and the diameter of the drill is therefore decreasing. When a hole having the above small diameter is made, the problem is that the drill bends or breaks or that the processing speed is low, due to the small diameter of the drill, which results in problems in productivity and reliability.
Further, when there is employed a method in which holes having the same size are made in copper foils on front and reverse surfaces through negative films according to a predetermined method, further, a copper foil having similar holes made by etching is disposed as an internal layer copper foil and a hole for a through hole reaching the front and reverse surfaces is made with a carbon dioxide gas laser, the problems are that the deviation of the position of the internal copper foil occurs and that the positions of the holes on the upper and lower surfaces deviate from each other so that a failure in connection occurs and it is difficult to form lands on the front and reverse surfaces.
Further, when a high-density printed wiring board is prepared, a generally known method is a photo via method and a laser via method. These methods are a xe2x80x9cbuild-upxe2x80x9d method in which each layer is connected to another layer with a blind via hole and laminated. In this method, upper and lower layers are built-up one stage by one stage so that process steps are complicated, workability is poor and the price of a board obtained according to this method is expensive. Further, when a high-density printed wiring board is prepared by the use of only a mechanical drill so as to arrange a hole-hole distance to be 100 to 150 xcexcm, cracks of a glass fiber occur due to the drill and plating is impregnated so that anti-migration properties are poor.
It is an object of the present invention to provide a high-density printed wiring board comprising a copper-clad multi-layered board having excellent reliability, productivity and economic performance, which multi-layered board is obtained by making a hole in a multi-layered copper-clad board having at least three copper foil layers with a carbon dioxide gas laser, and a method of producing it.
It is another object of the present invention to provide a high-density printed wiring board which is free from the occurrence of failures such as a short circuit and a pattern breakage in the formation of front and reverse circuits, and a method of producing it.
It is further another object of the present invention to provide a high-density printed wiring board which is also excellent in electric insulation properties, anti-migration properties and heat resistance, and a method of producing it.
According to the present invention, there is provided a high-density multi-layered printed wiring board including a copper-clad multi-layered board having a hole having a diameter of 25 to 200 xcexcm, and includes at least three copper foil layers,
wherein at least one hole is made with a laser and all connections between copper foil layers are done with a through-hole perforating through each of the copper foil layers.
According to the present invention, there is provided a method of producing a multi-layered printed wiring board which comprises a copper-clad multi-layered board obtained by forming a penetration hole in a multi-layered board having at least three copper foil layers, by direct irradiation with an energy sufficient for removing the copper foil by means of the pulse oscillation of the carbon dioxide gas laser,
wherein the copper-clad multi-layered board is obtained by disposing a coating or a sheet, of a resin composition layer containing 3 to 97% by volume of a least one powder selected from the group consisting of a metal compound powder which has a melting point of at least 900xc2x0 C. and a bond energy of at least 300 KJ/mol, a carbon powder, and metal powder, as an auxiliary material for making a hole, on a copper foil surface or treating the copper foil surface to form a metal oxide. Thereafter, the resultant surface is directly irradiated with a carbon dioxide gas laser to form a hole penetrating through the copper foil of the front and reverse copper foil layers and of the internal copper foil layer(s), then dissolving and removing copper foil burrs from the front and reverse copper foil layers and from the internal copper foil layer(s) (copper foil burrs include copper foil that overhang on the penetration hole portion) with a chemical, and carrying out plating with copper.
According to the present invention, there is provided a method of producing a multi-layered printed wiring board according to the above method, wherein the auxiliary material for making a hole is prepared by disposing a coating or a sheet of a resin composition containing 3 to 97% by volume of at least one powder selected from the group consisting of a metal compound powder, a carbon powder and metal powder which have a melting point of at least 900xc2x0 C. and a bond energy of at least 300 KJ/mol and having a carboxyl group in its molecule, on the copper foil surface.